This invention relates to the prevention of grounding accidents for marine vessels, and in particular submersible vessels such as, for example, submarines; when operating below the surface. Grounding accidents are a major risk for submarines and other submersibles which must operate in confined underwater channels. Furthermore, in submersible accidents the potential for hull loss and loss of life increases dramatically over those associated with grounding of surface vessels.
Despite the significant risk there exist limited systems for the prevention of grounding accidents. Most submersibles are equipped with sonar to monitor the actual depth of the water beneath the hull. However, this device is a reactive system that provides only a current status and does not protect against anticipated conditions present along the projected track of the boat. This device also requires active monitoring by ship""s crew to detect a hazardous condition. In military operations, use of the sonar may inadvertently betray the boat""s location to enemy vessels.
Submarines may also be equipped with moving map displays that show the vessel""s progress relative to a stored nautical chart. These systems also require the crew to actively monitor the vessel""s progress against the chart and to proactively identify hazardous conditions.
In the aviation industry various systems have been developed that provide warnings and advisory indications to the pilot of aircraft approaching hazardous terrain. Among such systems are systems generally known as ground proximity warning systems (GPWS) which monitor the flight conditions of an aircraft and provide a warning if flight conditions are such that inadvertent contact with terrain is imminent. Among the flight conditions normally monitored by such systems are radio altitude and rate, barometric altitude and rate, air speed, flap and gear positions. These parameters are monitored and an advisory signal and/or warning signal is generated when the relationship between the parameters is such that terrain impact is likely to occur. Typical examples of such systems are disclosed in U.S. Pat. Nos. 3,715,718; 3,936,796; 3,958,218; 3,944,968; 3,947,808; 3,947,810; 3,934,221; 3,958,219; 3,925,751; 3,934,222; 4,060,793; 4,030,065; 4,215,334; and 4,319,218, all assigned to the same assignee as the assignee of the present invention and hereby incorporated by reference. U.S. Pat. Nos. 5,488,563 and 5,839,080 to Mueller et al. each disclose a controlled flight into terrain alerting system that utilizes a terrain database in conjunction with aircraft dynamics to alert pilots of dangerous proximity to terrain.
However, such systems are designed for aircraft wherein the escape maneuver chiefly consists of adding full power and pitching the aircraft up to initiate a climb. This type of escape has limited utility for a submarine whose chief purpose is to stay concealed by remaining submerged. U.S. Pat. No. 5,488,563 to Chazelle describes a ground proximity warning system for aircraft that suggests a turning maneuver to escape terrain. However, Chazelle does not disclose or suggest how such a system could be applied to ships, submarines or boats.
U.S. Pat. No. 4,646,244 to Bateman discloses a terrain alerting methodology which may be applied to submarines. However, this reference does not discuss terrain avoidance procedures and in particular terrain avoidance procedures for submarines.
The present invention includes recognition of the need to provide marine vessels with an alert of conditions that may lead to an inadvertent grounding. The alerts provided by the present invention may be either reactive and/or predictive.
According to one aspect of the present invention, the ship""s sonar is utilized to provide an indication of impending impact with bottom obstructions based upon rate of change of depth beneath the keel.
According to another aspect of the invention, an ocean bottom terrain data base is provided. The ship""s position and anticipated track and/or instantaneous heading vector are compared to the ocean bottom terrain data and an alert is provided when a hazardous condition is detected.
According to another aspect of the invention, ocean bottom hazards are displayed on a visual display representative of a plan view of the ocean or waterway bottom terrain. Preferably the terrain is displayed in various colors and/or dot pattern densities depending upon the degree of grounding hazard to the vessel. In a preferred embodiment of the invention, the terrain that does not present a hazard to the vessel is displayed in a first color, terrain that is a potential hazard to the vessel is displayed as second color and terrain which represents an immediate and actual danger to the vessel is colored a third color.
More specifically, the bottom proximity awareness system comprises a navigational system configured to determine latitude, longitude, depth, points of intended movement, and speed of a vessel employing the system. The navigational system generates signals in response to the listed parameters. The system further comprises: a terrain database comprising depth data for underwater terrain and obstacle information as well as for port facilities; a processor configured to identify from the terrain database depth data within a range of the vessel; warning envelope generator; and a warning device. Further advantages and features of the present invention will be described in detail below.